1. Field of the Invention
The present invention relates to data processing, and, in particular, to measures for characterizing compressed video and audio bitstreams.
2. Description of the Related Art
It is known to compress digital video and audio signals for storage and/or transmission for subsequent and/or remote decompression and playback. Algorithms for performing such digital video and audio compression are specified by various groups, such as the Motion Picture Experts Group (MPEG). MPEG standard algorithms, such as MPEG-2 , are defined in terms of the syntax of the bitstreams and the process for decoding those bitstreams. Encoders conforming to these standards must be able to generate bitstreams with the defined syntax. Nevertheless, the exact processing implemented by such encoders might not be specified by the standards and can therefore vary from encoder to encoder. Moreover, some encoders can be controlled to generate bitstreams for different applications, such as high-quality playback, which may involve relatively large bitstreams, or real-time transmission, which may involve relatively small bitstreams. Thus, for example, two different MPEG video encoders may generate two different bitstreams from the same digital video input stream, with each bitstream conforming to the syntax rules specified by the MPEG video standard.
Because of this variability in encoding, it is useful to provide measures for characterizing compressed bitstreams, such as the video and audio bitstreams that conform to the MPEG standards. Such measures may provide objective indicators of the relative quality between bitstreams generated by different encoders. Such objective measures may prove even more useful than a direct comparison of the decompressed streams at playback. Moreover, such measures provide an objective mechanism for comparing the quality and other characteristics of compressed bitstreams generated from different input signals.